duke@435: /*
ysr@2647:  * Copyright (c) 2001, 2011, Oracle and/or its affiliates. All rights reserved.
duke@435:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
duke@435:  *
duke@435:  * This code is free software; you can redistribute it and/or modify it
duke@435:  * under the terms of the GNU General Public License version 2 only, as
duke@435:  * published by the Free Software Foundation.
duke@435:  *
duke@435:  * This code is distributed in the hope that it will be useful, but WITHOUT
duke@435:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
duke@435:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
duke@435:  * version 2 for more details (a copy is included in the LICENSE file that
duke@435:  * accompanied this code).
duke@435:  *
duke@435:  * You should have received a copy of the GNU General Public License version
duke@435:  * 2 along with this work; if not, write to the Free Software Foundation,
duke@435:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
duke@435:  *
trims@1907:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
trims@1907:  * or visit www.oracle.com if you need additional information or have any
trims@1907:  * questions.
duke@435:  *
duke@435:  */
duke@435: 
stefank@2314: #ifndef SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
stefank@2314: #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
stefank@2314: 
stefank@2314: #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
stefank@2314: #include "gc_implementation/shared/concurrentGCThread.hpp"
stefank@2314: #ifdef TARGET_OS_FAMILY_linux
stefank@2314: # include "thread_linux.inline.hpp"
stefank@2314: #endif
stefank@2314: #ifdef TARGET_OS_FAMILY_solaris
stefank@2314: # include "thread_solaris.inline.hpp"
stefank@2314: #endif
stefank@2314: #ifdef TARGET_OS_FAMILY_windows
stefank@2314: # include "thread_windows.inline.hpp"
stefank@2314: #endif
never@3156: #ifdef TARGET_OS_FAMILY_bsd
never@3156: # include "thread_bsd.inline.hpp"
never@3156: #endif
stefank@2314: 
duke@435: class ConcurrentMarkSweepGeneration;
duke@435: class CMSCollector;
duke@435: 
ysr@2647: // The Concurrent Mark Sweep GC Thread
duke@435: class ConcurrentMarkSweepThread: public ConcurrentGCThread {
duke@435:   friend class VMStructs;
duke@435:   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
duke@435:   friend class CMSCollector;
duke@435:  public:
duke@435:   virtual void run();
duke@435: 
duke@435:  private:
duke@435:   static ConcurrentMarkSweepThread*     _cmst;
duke@435:   static CMSCollector*                  _collector;
duke@435:   static SurrogateLockerThread*         _slt;
duke@435:   static SurrogateLockerThread::SLT_msg_type _sltBuffer;
duke@435:   static Monitor*                       _sltMonitor;
duke@435: 
duke@435:   static bool _should_terminate;
duke@435: 
duke@435:   enum CMS_flag_type {
duke@435:     CMS_nil             = NoBits,
duke@435:     CMS_cms_wants_token = nth_bit(0),
duke@435:     CMS_cms_has_token   = nth_bit(1),
duke@435:     CMS_vm_wants_token  = nth_bit(2),
duke@435:     CMS_vm_has_token    = nth_bit(3)
duke@435:   };
duke@435: 
duke@435:   static int _CMS_flag;
duke@435: 
duke@435:   static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }
duke@435:   static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }
duke@435:   static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }
duke@435:   void sleepBeforeNextCycle();
duke@435: 
duke@435:   // CMS thread should yield for a young gen collection, direct allocation,
duke@435:   // and iCMS activity.
duke@435:   static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing
duke@435:   static volatile jint _pending_yields;
duke@435:   static volatile jint _pending_decrements; // decrements to _pending_yields
duke@435:   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing
duke@435: 
duke@435:   // Tracing messages, enabled by CMSTraceThreadState.
duke@435:   static inline void trace_state(const char* desc);
duke@435: 
ysr@2647:   static volatile int _icms_disabled;   // a counter to track #iCMS disable & enable
duke@435:   static volatile bool _should_run;     // iCMS may run
duke@435:   static volatile bool _should_stop;    // iCMS should stop
duke@435: 
duke@435:   // debugging
duke@435:   void verify_ok_to_terminate() const PRODUCT_RETURN;
duke@435: 
duke@435:  public:
duke@435:   // Constructor
duke@435:   ConcurrentMarkSweepThread(CMSCollector* collector);
duke@435: 
duke@435:   static void makeSurrogateLockerThread(TRAPS);
duke@435:   static SurrogateLockerThread* slt() { return _slt; }
duke@435: 
duke@435:   // Tester
duke@435:   bool is_ConcurrentGC_thread() const { return true;       }
duke@435: 
duke@435:   static void threads_do(ThreadClosure* tc);
duke@435: 
duke@435:   // Printing
duke@435:   void print_on(outputStream* st) const;
duke@435:   void print() const                                  { print_on(tty); }
duke@435:   static void print_all_on(outputStream* st);
duke@435:   static void print_all()                             { print_all_on(tty); }
duke@435: 
duke@435:   // Returns the CMS Thread
duke@435:   static ConcurrentMarkSweepThread* cmst()    { return _cmst; }
duke@435:   static CMSCollector*         collector()    { return _collector;  }
duke@435: 
duke@435:   // Create and start the CMS Thread, or stop it on shutdown
duke@435:   static ConcurrentMarkSweepThread* start(CMSCollector* collector);
duke@435:   static void stop();
duke@435:   static bool should_terminate() { return _should_terminate; }
duke@435: 
duke@435:   // Synchronization using CMS token
duke@435:   static void synchronize(bool is_cms_thread);
duke@435:   static void desynchronize(bool is_cms_thread);
duke@435:   static bool vm_thread_has_cms_token() {
duke@435:     return CMS_flag_is_set(CMS_vm_has_token);
duke@435:   }
duke@435:   static bool cms_thread_has_cms_token() {
duke@435:     return CMS_flag_is_set(CMS_cms_has_token);
duke@435:   }
duke@435:   static bool vm_thread_wants_cms_token() {
duke@435:     return CMS_flag_is_set(CMS_vm_wants_token);
duke@435:   }
duke@435:   static bool cms_thread_wants_cms_token() {
duke@435:     return CMS_flag_is_set(CMS_cms_wants_token);
duke@435:   }
duke@435: 
duke@435:   // Wait on CMS lock until the next synchronous GC
ysr@2242:   // or given timeout, whichever is earlier. A timeout value
ysr@2242:   // of 0 indicates that there is no upper bound on the wait time.
ysr@2242:   // A concurrent full gc request terminates the wait.
ysr@2242:   void wait_on_cms_lock(long t_millis);
duke@435: 
ysr@2192:   // The CMS thread will yield during the work portion of its cycle
duke@435:   // only when requested to.  Both synchronous and asychronous requests
ysr@2192:   // are provided:
ysr@2192:   // (1) A synchronous request is used for young gen collections and
ysr@2192:   //     for direct allocations.  The requesting thread increments
ysr@2192:   //     _pending_yields at the beginning of an operation, and decrements
ysr@2192:   //     _pending_yields when that operation is completed.
ysr@2192:   //     In turn, the CMS thread yields when _pending_yields is positive,
ysr@2192:   //     and continues to yield until the value reverts to 0.
ysr@2192:   // (2) An asynchronous request, on the other hand, is used by iCMS
ysr@2192:   //     for the stop_icms() operation. A single yield satisfies all of
ysr@2192:   //     the outstanding asynch yield requests, of which there may
ysr@2192:   //     occasionally be several in close succession. To accomplish
ysr@2192:   //     this, an asynch-requesting thread atomically increments both
ysr@2192:   //     _pending_yields and _pending_decrements. An asynchr requesting
ysr@2192:   //     thread does not wait and "acknowledge" completion of an operation
ysr@2192:   //     and deregister the request, like the synchronous version described
ysr@2192:   //     above does. In turn, after yielding, the CMS thread decrements both
ysr@2192:   //     _pending_yields and _pending_decrements by the value seen in
ysr@2192:   //     _pending_decrements before the decrement.
ysr@2192:   //  NOTE: The above scheme is isomorphic to having two request counters,
ysr@2192:   //  one for async requests and one for sync requests, and for the CMS thread
ysr@2192:   //  to check the sum of the two counters to decide whether it should yield
ysr@2192:   //  and to clear only the async counter when it yields. However, it turns out
ysr@2192:   //  to be more efficient for CMS code to just check a single counter
ysr@2192:   //  _pending_yields that holds the sum (of both sync and async requests), and
ysr@2192:   //  a second counter _pending_decrements that only holds the async requests,
ysr@2192:   //  for greater efficiency, since in a typical CMS run, there are many more
ysr@2192:   //  pontential (i.e. static) yield points than there are actual
ysr@2192:   //  (i.e. dynamic) yields because of requests, which are few and far between.
ysr@2192:   //
duke@435:   // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
duke@435:   // we cannot easily test that invariant, since the counters are manipulated via
duke@435:   // atomic instructions without explicit locking and we cannot read
duke@435:   // the two counters atomically together: one suggestion is to
duke@435:   // use (for example) 16-bit counters so as to be able to read the
duke@435:   // two counters atomically even on 32-bit platforms. Notice that
ysr@2192:   // the second assert in acknowledge_yield_request() below does indeed
duke@435:   // check a form of the above invariant, albeit indirectly.
duke@435: 
duke@435:   static void increment_pending_yields()   {
duke@435:     Atomic::inc(&_pending_yields);
duke@435:     assert(_pending_yields >= 0, "can't be negative");
duke@435:   }
duke@435:   static void decrement_pending_yields()   {
duke@435:     Atomic::dec(&_pending_yields);
duke@435:     assert(_pending_yields >= 0, "can't be negative");
duke@435:   }
duke@435:   static void asynchronous_yield_request() {
ysr@2192:     assert(CMSIncrementalMode, "Currently only used w/iCMS");
duke@435:     increment_pending_yields();
duke@435:     Atomic::inc(&_pending_decrements);
duke@435:     assert(_pending_decrements >= 0, "can't be negative");
duke@435:   }
duke@435:   static void acknowledge_yield_request() {
duke@435:     jint decrement = _pending_decrements;
duke@435:     if (decrement > 0) {
ysr@2192:       assert(CMSIncrementalMode, "Currently only used w/iCMS");
duke@435:       // Order important to preserve: _pending_yields >= _pending_decrements
duke@435:       Atomic::add(-decrement, &_pending_decrements);
duke@435:       Atomic::add(-decrement, &_pending_yields);
duke@435:       assert(_pending_decrements >= 0, "can't be negative");
duke@435:       assert(_pending_yields >= 0, "can't be negative");
duke@435:     }
duke@435:   }
duke@435:   static bool should_yield()   { return _pending_yields > 0; }
duke@435: 
duke@435:   // CMS incremental mode.
duke@435:   static void start_icms(); // notify thread to start a quantum of work
duke@435:   static void stop_icms();  // request thread to stop working
duke@435:   void icms_wait();         // if asked to stop, wait until notified to start
duke@435: 
duke@435:   // Incremental mode is enabled globally by the flag CMSIncrementalMode.  It
duke@435:   // must also be enabled/disabled dynamically to allow foreground collections.
ysr@2647: #define ICMS_ENABLING_ASSERT                                                      \
ysr@2647:           assert((CMSIncrementalMode  && _icms_disabled >= 0) ||                  \
ysr@2647:                  (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
ysr@2647: 
ysr@2647:   static inline void enable_icms() {
ysr@2647:     ICMS_ENABLING_ASSERT;
ysr@2647:     Atomic::dec(&_icms_disabled);
ysr@2647:   }
ysr@2647:   static inline void disable_icms() {
ysr@2647:    ICMS_ENABLING_ASSERT;
ysr@2647:    Atomic::inc(&_icms_disabled);
ysr@2647:   }
ysr@2647:   static inline bool icms_is_disabled() {
ysr@2647:    ICMS_ENABLING_ASSERT;
ysr@2647:    return _icms_disabled > 0;
ysr@2647:   }
ysr@2647:   static inline bool icms_is_enabled() {
ysr@2647:    return !icms_is_disabled();
ysr@2647:   }
duke@435: };
duke@435: 
duke@435: inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
duke@435:   if (CMSTraceThreadState) {
duke@435:     char buf[128];
duke@435:     TimeStamp& ts = gclog_or_tty->time_stamp();
duke@435:     if (!ts.is_updated()) {
duke@435:       ts.update();
duke@435:     }
duke@435:     jio_snprintf(buf, sizeof(buf), " [%.3f:  CMSThread %s] ",
duke@435:                  ts.seconds(), desc);
duke@435:     buf[sizeof(buf) - 1] = '\0';
duke@435:     gclog_or_tty->print(buf);
duke@435:   }
duke@435: }
duke@435: 
ysr@2192: // For scoped increment/decrement of (synchronous) yield requests
duke@435: class CMSSynchronousYieldRequest: public StackObj {
duke@435:  public:
duke@435:   CMSSynchronousYieldRequest() {
duke@435:     ConcurrentMarkSweepThread::increment_pending_yields();
duke@435:   }
duke@435:   ~CMSSynchronousYieldRequest() {
duke@435:     ConcurrentMarkSweepThread::decrement_pending_yields();
duke@435:   }
duke@435: };
duke@435: 
duke@435: // Used to emit a warning in case of unexpectedly excessive
duke@435: // looping (in "apparently endless loops") in CMS code.
duke@435: class CMSLoopCountWarn: public StackObj {
duke@435:  private:
duke@435:   const char* _src;
duke@435:   const char* _msg;
duke@435:   const intx  _threshold;
duke@435:   intx        _ticks;
duke@435: 
duke@435:  public:
duke@435:   inline CMSLoopCountWarn(const char* src, const char* msg,
duke@435:                           const intx threshold) :
duke@435:     _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
duke@435: 
duke@435:   inline void tick() {
duke@435:     _ticks++;
duke@435:     if (CMSLoopWarn && _ticks % _threshold == 0) {
duke@435:       warning("%s has looped %d times %s", _src, _ticks, _msg);
duke@435:     }
duke@435:   }
duke@435: };
stefank@2314: 
stefank@2314: #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP